1. Field of the Invention
This invention relates to mixing apparatus, and more particularly to mixing apparatus for mixing at least one material with a liquid.
2. Description of the Prior Art
Generally, mixing apparatus described in the prior art fall into one of two classes -- mixing apparatus which employ mechanical moving parts, such as motor driven rotors, propellors, etc., and mixing apparatus which do not have mechanical moving motor parts but instead rely on a forced fluid flow to accomplish mixing. Advantages of the latter type of mixing apparatus (flow energy mixing apparatus) over the former are well known. Mechanical mixing apparatus employ motors and other moving parts which are subject to wear and subsequent failure. Frequently, the chemicals being mixed, or vapors therefrom, are incompatible with the mechanical moving parts and thus directly induce mixer breakdown. Mechanical mixers also tend to generate substantial levels of noise which can be annoying if not disruptive to persons in the immediate vicinity of the mixer.
Flow-energy mixers are especially suited for mixing relatively small amounts (10 gallons or less) of miscible materials. The photographic field provides numerous examples wherein small amounts of miscible materials are mixed. For example, photographic processing solutions are often mixed in volumes from one to five gallons. In order for a flow-energy mixer to be of general utility in mixing a wide variety of materials, however, the mixer must possess certain properties -- some of which are not readily compatible with each other, and some of which are not readily compatible with flow-energy mixing in general. The problems involved in designing a fow-energy mixer of general utility can be pointed out by considering the properties of flow-energy mixers disclosed in the prior art.
One of the earliest flow-energy mixers disclosed in the prior art is described in U.S. Pat. No. 2,528,094. Mixing is accomplished in a tank provided with baffles. Liquid under pressure is forced through a nozzle and into the tank, wherein the baffles coact to create a condition of high turbulence. As disclosed in the patent, this high turbulence may require flow rates in excess of that available from conventional water outlets such as house faucets, and thus additional pumping may be required in order to supply the energy consumed by the mixing unit. In many applications, the use of an extra pump is not desirable. For a flow-energy mixing apparatus suitable for mixing photographic chemicals, particularly mixing which is done by the amateur photographer in his home, it is preferable to have a mixing apparatus that operates effectively from conventional water outlets. In addition, baffles of the type described in the above patent are provided to produce high turbulence, but also tend to introduce "dead spots" wherein no mixing or a reduced level of mixing occurs.
U.S. Pat. No. 3,799,508 discloses a flow-energy mixing apparatus wherein a mixing compartment contains a nozzle mounted near the bottom of a mixing compartment and directs a liquid flow outwardly and downwardly to agitate the liquid in the compartment. The level of mixing may not be uniform throughout the mixing compartment, necessitating extended mixing periods in order to ensure uniform and thorough mixing of the compartment contents.
A device for continuous mixing of materials is described in U.S. Pat. No. 3,661,364. The materials to be mixed are pumped into a tank, near the bottom, and exit through an outlet pipe located near the top of the tank. Mixing is accomplished in a doughnut shaped fluid flow pattern. While using flow-energy to achieve mixing, the disclosed device employs a pump through which chemicals to be mixed are pumped and as a result, possesses the previously mentioned disadvantages of a mechanical mixer.